Commercial construction systems have long contemplated the installation of acoustical ceilings. Positioned within, or forming a part of, such ceiling may be a number of items, such as light fixtures, sprinkler nozzles, and diffusers for cooling systems. Such diffusers provide openings for cool air produced by the system, such openings oftentimes being positioned adjacent a window. A diffuser normally is positioned intermediate a pair of spaced, parallel, main runners. These runners need be kept parallel for a number of reasons, including geometric symmetry and ease of fixture placement. Spacers have been developed in the past for fixidly positioning main runners in parallel relationship, and thereby stabilizing the diffuser openings. The present invention represents a spacer improved over the prior art in permitting both economy of fabrication and positive parallel alignment of the main runners.